Wilton climate

Wilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Wilton, 0.5 km from Wilton, elevation 2188 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wilton. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around May 11 and the first fall freeze around September 30, a growing season of about 142 days.

Median at 36°F
last May 20, first September 22
Median at 32°F
last May 11, first September 30
Median at 28°F
last May 1, first October 9

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 2May 29May 26May 23May 20May 18May 14May 12May 7
32°FMay 25May 20May 16May 13May 11May 8May 6May 3Apr 30
28°FMay 14May 9May 6May 3May 1Apr 29Apr 26Apr 22Apr 18
24°FMay 4May 1Apr 28Apr 24Apr 22Apr 19Apr 16Apr 13Apr 9
20°FApr 27Apr 22Apr 18Apr 16Apr 13Apr 10Apr 8Apr 5Apr 1
16°FApr 19Apr 15Apr 11Apr 9Apr 6Apr 4Apr 1Mar 29Mar 22

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 10Sep 14Sep 17Sep 19Sep 22Sep 25Sep 27Sep 30Oct 4
32°FSep 17Sep 22Sep 25Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12
28°FSep 25Sep 30Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 21
24°FOct 3Oct 8Oct 11Oct 14Oct 17Oct 20Oct 23Oct 26Oct 30
20°FOct 12Oct 16Oct 20Oct 23Oct 26Oct 29Nov 1Nov 4Nov 9
16°FOct 19Oct 25Oct 28Oct 31Nov 2Nov 5Nov 9Nov 12Nov 17

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F141135131127124120115110104
32°F159153149146142138134129122
28°F178171167162159156152148141
24°F196189185181177173169164157
20°F211206201198194191186181174
16°F229221217213209205201196190

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
9,210
Cooling degree days, base 65°F
373
Growing degree days, base 40°F
3,771
Growing degree days, base 45°F
2,855
Growing degree days, base 50°F
2,047
Growing degree days, base 55°F
1,353
Growing degree days, base 60°F
788

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,70200
February1,43400
March1,20801
April740028
May3628178
June12053385
July29149584
August48129546
September24134272
October677150
November1,11402
December1,53600

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 0.5 km from Wilton. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00329455 (Wilton). Public domain.